True, I guess I try to have some objective measures like my chess elo and maybe some canaries like what books I'm reading. But it would be really hard to tell.
Cognitive ability can be highly specific. If you don't use it you lose it. You may be able to keep your chess ELO high, but realize you can't implement basic algorithms in C++ quite as readily as you used to. Or you can't write as well as you used to. Or you can't quite make that old recipe taste as good as you remember.
We can argue about what skills are important or not, but these things tend to sneak up on us.
